feat: use nixos-rebuild build-image instead of nixosGenerators

lib/mkHost.nix

@@ -13,25 +13,25 @@ name:
 let
   hostConfig = ../hosts/${name}/configuration.nix;
   hostHWConfig = ../hosts/${name}/hardware-configuration.nix;
+  hasHWConfig = builtins.pathExists hostHWConfig;
 
   userHMConfigs = nixpkgs.lib.genAttrs users (
     user: import ../users/${user}/home-manager.nix { inherit inputs; }
   );
 
 in
-
 nixpkgs.lib.nixosSystem {
   inherit system;
   modules = [
-
     ../nix.nix
 
     { nixpkgs.overlays = overlays; }
     { nixpkgs.config.allowUnfree = true; }
 
     hostConfig
-    hostHWConfig
-
+  ]
+  ++ nixpkgs.lib.optional hasHWConfig hostHWConfig
+  ++ [
     inputs.home-manager.nixosModules.home-manager
     {
       home-manager.useGlobalPkgs = true;
@@ -39,7 +39,6 @@ nixpkgs.lib.nixosSystem {
       home-manager.users = userHMConfigs;
       home-manager.extraSpecialArgs = { inherit inputs; };
     }
-
   ];
   specialArgs = { inherit inputs; };
 }